Commit d5ad50bd authored by Mikhail Fludkov's avatar Mikhail Fludkov Committed by Mathieu Duponchelle

rtp: Implement ULPFEC (RFC 5109)

We expose a set of new elements:

* ULPFEC encoder / decoder
* A storage element, which should be placed before jitterbuffers,
  and is used to store packets in order to attempt reconstruction
  after the jitterbuffer has sent PacketLost events
* RED encoder / decoder (RFC 2198), these are necessary to
  use FEC in webrtc, as browsers will propose and expect ulpfec
  packets to be wrapped in red packets

With contributions from:

Mathieu Duponchelle <mathieu@centricular.com>
Sebastian Dröge <sebastian@centricular.com>

https://bugzilla.gnome.org/show_bug.cgi?id=792696
parent 82d09502
......@@ -93,7 +93,16 @@ libgstrtp_la_SOURCES = \
gstrtpvrawpay.c \
gstrtpstreampay.c \
gstrtpstreamdepay.c \
gstrtputils.c
gstrtputils.c \
rtpulpfeccommon.c \
gstrtpulpfecdec.c \
gstrtpulpfecenc.c \
rtpredcommon.c \
gstrtpredenc.c \
gstrtpreddec.c \
rtpstorage.c \
rtpstoragestream.c \
gstrtpstorage.c
libgstrtp_la_CFLAGS = $(GST_PLUGINS_BASE_CFLAGS) $(GST_BASE_CFLAGS) \
$(GST_CFLAGS) -Dvp8_norm=gst_rtpvp8_vp8_norm \
......
......@@ -113,6 +113,13 @@
#include "gstrtpvrawpay.h"
#include "gstrtpstreampay.h"
#include "gstrtpstreamdepay.h"
#include "gstrtpredenc.h"
#include "gstrtpreddec.h"
#include "gstrtpulpfecdec.h"
#include "gstrtpulpfecenc.h"
#include "gstrtpreddec.h"
#include "gstrtpredenc.h"
#include "gstrtpstorage.h"
static gboolean
plugin_init (GstPlugin * plugin)
......@@ -388,6 +395,34 @@ plugin_init (GstPlugin * plugin)
if (!gst_rtp_stream_depay_plugin_init (plugin))
return FALSE;
if (!gst_element_register (plugin, "rtpredenc", GST_RANK_NONE,
GST_TYPE_RTP_RED_ENC))
return FALSE;
if (!gst_element_register (plugin, "rtpreddec", GST_RANK_NONE,
GST_TYPE_RTP_RED_DEC))
return FALSE;
if (!gst_element_register (plugin, "rtpulpfecdec", GST_RANK_NONE,
GST_TYPE_RTP_ULPFEC_DEC))
return FALSE;
if (!gst_element_register (plugin, "rtpulpfecenc", GST_RANK_NONE,
GST_TYPE_RTP_ULPFEC_ENC))
return FALSE;
if (!gst_element_register (plugin, "rtpreddec", GST_RANK_NONE,
GST_TYPE_RTP_RED_DEC))
return FALSE;
if (!gst_element_register (plugin, "rtpredenc", GST_RANK_NONE,
GST_TYPE_RTP_RED_ENC))
return FALSE;
if (!gst_element_register (plugin, "rtpstorage", GST_RANK_NONE,
GST_TYPE_RTP_STORAGE))
return FALSE;
return TRUE;
}
......
/* GStreamer plugin for forward error correction
* Copyright (C) 2017 Pexip
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*
* Author: Mikhail Fludkov <misha@pexip.com>
*/
#include <gst/rtp/gstrtpbuffer.h>
#include "rtpredcommon.h"
#include "gstrtpreddec.h"
#include "rtpulpfeccommon.h"
#define RTP_HISTORY_MAX_SIZE (16)
typedef struct
{
guint32 timestamp;
guint16 seq;
} RTPHistItem;
#define RTP_HIST_ITEM_TIMESTAMP(p) ((RTPHistItem *)p)->timestamp
#define RTP_HIST_ITEM_SEQ(p) ((RTPHistItem *)p)->seq
static GstStaticPadTemplate sink_template = GST_STATIC_PAD_TEMPLATE ("sink",
GST_PAD_SINK,
GST_PAD_ALWAYS,
GST_STATIC_CAPS ("application/x-rtp"));
static GstStaticPadTemplate src_template = GST_STATIC_PAD_TEMPLATE ("src",
GST_PAD_SRC,
GST_PAD_ALWAYS,
GST_STATIC_CAPS ("application/x-rtp"));
#define UNDEF_PT -1
#define MIN_PT UNDEF_PT
#define MAX_PT 127
#define DEFAULT_PT UNDEF_PT
GST_DEBUG_CATEGORY_STATIC (gst_rtp_red_dec_debug);
#define GST_CAT_DEFAULT (gst_rtp_red_dec_debug)
G_DEFINE_TYPE (GstRtpRedDec, gst_rtp_red_dec, GST_TYPE_ELEMENT);
enum
{
PROP_0,
PROP_PT,
PROP_RECEIVED
};
static RTPHistItem *
rtp_hist_item_alloc (void)
{
return g_slice_new (RTPHistItem);
}
static void
rtp_hist_item_free (gpointer item)
{
g_slice_free (RTPHistItem, item);
}
static gint
gst_rtp_red_history_find_less_or_equal (gconstpointer item,
gconstpointer timestamp)
{
guint32 t = GPOINTER_TO_UINT (timestamp);
gint32 diff = t - RTP_HIST_ITEM_TIMESTAMP (item);
return diff < 0;
}
static gint
gst_rtp_red_history_find_less (gconstpointer item, gconstpointer timestamp)
{
guint32 t = GPOINTER_TO_UINT (timestamp);
gint32 diff = t - RTP_HIST_ITEM_TIMESTAMP (item);
return diff <= 0;
}
static void
gst_rtp_red_history_update (GstRtpRedDec * self, GstRTPBuffer * rtp)
{
RTPHistItem *item;
GList *link, *sibling;
/* If we have not reached MAX number of elements in the history,
* allocate a new link and a new item,
* otherwise reuse the tail (the oldest data) without any reallocations
*/
if (self->rtp_history->length < RTP_HISTORY_MAX_SIZE) {
item = rtp_hist_item_alloc ();
link = g_list_alloc ();
link->data = item;
} else {
link = g_queue_pop_tail_link (self->rtp_history);
item = link->data;
}
item->timestamp = gst_rtp_buffer_get_timestamp (rtp);
item->seq = gst_rtp_buffer_get_seq (rtp);
/* Looking for a place to insert new link.
* The queue has newest to oldest rtp timestamps, so in 99% cases
* it is inserted before the head of the queue */
sibling = g_list_find_custom (self->rtp_history->head,
GUINT_TO_POINTER (item->timestamp),
gst_rtp_red_history_find_less_or_equal);
g_queue_push_nth_link (self->rtp_history,
g_list_position (self->rtp_history->head, sibling), link);
}
static gboolean
rtp_red_buffer_is_valid (GstRtpRedDec * self, GstRTPBuffer * red_rtp,
gsize * dst_first_red_payload_offset)
{
guint8 *payload = gst_rtp_buffer_get_payload (red_rtp);
gsize payload_len = gst_rtp_buffer_get_payload_len (red_rtp);
gsize red_hdrs_offset = 0;
guint red_hdrs_checked = 0;
guint redundant_payload_len = 0;
while (TRUE) {
gpointer red_hdr = payload + red_hdrs_offset;
gsize red_hdr_len;
gboolean is_redundant;
++red_hdrs_checked;
/* Can we address the first byte where F bit is located ? */
if (red_hdrs_offset + 1 > payload_len)
goto red_buffer_invalid;
is_redundant = rtp_red_block_is_redundant (red_hdr);
/* Is it the last block? */
if (is_redundant) {
red_hdr_len = rtp_red_block_header_get_length (TRUE);
/* Can we address all the other bytes in RED block header? */
if (red_hdrs_offset + red_hdr_len > payload_len)
goto red_buffer_invalid;
redundant_payload_len += rtp_red_block_get_payload_length (red_hdr);
red_hdrs_offset += red_hdr_len;
} else {
red_hdr_len = rtp_red_block_header_get_length (FALSE);
red_hdrs_offset += red_hdr_len;
break;
}
}
/* Do we have enough data to create redundant packets & main packet. Keep in
* mind that redundant_payload_len contains the length of redundant packets only.
*/
if (red_hdrs_offset + redundant_payload_len >= payload_len)
goto red_buffer_invalid;
*dst_first_red_payload_offset = red_hdrs_offset;
GST_LOG_OBJECT (self, "RED packet has %u blocks", red_hdrs_checked);
return TRUE;
red_buffer_invalid:
GST_WARNING_OBJECT (self, "Received invalid RED packet "
"ssrc=0x%08x pt=%u tstamp=%u seq=%u size=%u, "
"checked %u blocks",
gst_rtp_buffer_get_ssrc (red_rtp),
gst_rtp_buffer_get_payload_type (red_rtp),
gst_rtp_buffer_get_timestamp (red_rtp),
gst_rtp_buffer_get_seq (red_rtp),
gst_rtp_buffer_get_packet_len (red_rtp), red_hdrs_checked);
return FALSE;
}
static gboolean
gst_red_history_lost_seq_num_for_timestamp (GstRtpRedDec * self,
guint32 timestamp, guint16 * dst_seq_num)
{
GList *older_sibling = g_list_find_custom (self->rtp_history->head,
GUINT_TO_POINTER (timestamp),
gst_rtp_red_history_find_less);
RTPHistItem *older;
RTPHistItem *newer;
guint32 timestamp_diff;
gint seq_diff;
if (NULL == older_sibling) {
if (self->rtp_history->length == RTP_HISTORY_MAX_SIZE)
GST_WARNING_OBJECT (self, "History is too short. "
"Oldest rtp timestamp %u, looking for %u, size %u",
RTP_HIST_ITEM_TIMESTAMP (self->rtp_history->tail->data),
timestamp, self->rtp_history->length);
return FALSE;
}
if (NULL == older_sibling->prev) {
GST_WARNING_OBJECT (self, "RED block timestamp offset probably wrong. "
"Latest rtp timestamp %u, looking for %u, size %u",
RTP_HIST_ITEM_TIMESTAMP (self->rtp_history->head->data),
timestamp, self->rtp_history->length);
return FALSE;
}
older = older_sibling->data;
newer = older_sibling->prev->data;
/* We know for sure @older has lower timestamp than we are looking for,
* if @newer has the same timestamp, there is no packet loss and we
* don't need to use redundant data */
if (newer->timestamp == timestamp)
return FALSE;
seq_diff = gst_rtp_buffer_compare_seqnum (older->seq, newer->seq);
if (seq_diff <= 1) {
if (seq_diff == 1)
GST_WARNING_OBJECT (self, "RED block timestamp offset is wrong: "
"#%u,%u #%u,%u looking for %u",
older->seq, older->timestamp,
newer->seq, newer->timestamp, timestamp);
else
GST_WARNING_OBJECT (self, "RTP timestamps increasing while "
"sequence numbers decreasing: #%u,%u #%u,%u",
older->seq, older->timestamp, newer->seq, newer->timestamp);
return FALSE;
}
timestamp_diff = newer->timestamp - older->timestamp;
for (gint lost_packet_idx = 1; lost_packet_idx < seq_diff; ++lost_packet_idx) {
guint32 lost_timestamp = older->timestamp +
lost_packet_idx * timestamp_diff / seq_diff;
if (lost_timestamp == timestamp) {
*dst_seq_num = older->seq + lost_packet_idx;
return TRUE;
}
}
GST_WARNING_OBJECT (self, "Can't find RED block timestamp "
"#%u,%u #%u,%u looking for %u",
older->seq, older->timestamp, newer->seq, newer->timestamp, timestamp);
return FALSE;
}
static GstBuffer *
gst_rtp_red_create_packet (GstRtpRedDec * self, GstRTPBuffer * red_rtp,
gboolean marker, guint8 pt, guint16 seq_num, guint32 timestamp,
gsize red_payload_subbuffer_start, gsize red_payload_subbuffer_len)
{
guint csrc_count = gst_rtp_buffer_get_csrc_count (red_rtp);
GstBuffer *ret = gst_rtp_buffer_new_allocate (0, 0, csrc_count);
GstRTPBuffer ret_rtp = GST_RTP_BUFFER_INIT;
if (!gst_rtp_buffer_map (ret, GST_MAP_WRITE, &ret_rtp))
g_assert_not_reached ();
gst_rtp_buffer_set_marker (&ret_rtp, marker);
gst_rtp_buffer_set_payload_type (&ret_rtp, pt);
gst_rtp_buffer_set_seq (&ret_rtp, seq_num);
gst_rtp_buffer_set_timestamp (&ret_rtp, timestamp);
gst_rtp_buffer_set_ssrc (&ret_rtp, gst_rtp_buffer_get_ssrc (red_rtp));
for (guint i = 0; i < csrc_count; ++i)
gst_rtp_buffer_set_csrc (&ret_rtp, i, gst_rtp_buffer_get_csrc (red_rtp, i));
gst_rtp_buffer_unmap (&ret_rtp);
ret = gst_buffer_append (ret,
gst_rtp_buffer_get_payload_subbuffer (red_rtp,
red_payload_subbuffer_start, red_payload_subbuffer_len));
/* Timestamps, meta, flags from the RED packet should go to main block packet */
gst_buffer_copy_into (ret, red_rtp->buffer, GST_BUFFER_COPY_METADATA, 0, -1);
return ret;
}
static GstBuffer *
gst_rtp_red_create_from_redundant_block (GstRtpRedDec * self,
GstRTPBuffer * red_rtp, gsize * red_hdr_offset, gsize * red_payload_offset)
{
guint8 *payload = gst_rtp_buffer_get_payload (red_rtp);
guint8 *red_hdr = payload + *red_hdr_offset;
guint32 lost_timestamp = gst_rtp_buffer_get_timestamp (red_rtp) -
rtp_red_block_get_timestamp_offset (red_hdr);
GstBuffer *ret = NULL;
guint16 lost_seq = 0;
if (gst_red_history_lost_seq_num_for_timestamp (self, lost_timestamp,
&lost_seq)) {
ret =
gst_rtp_red_create_packet (self, red_rtp, FALSE,
rtp_red_block_get_payload_type (red_hdr), lost_seq, lost_timestamp,
*red_payload_offset, rtp_red_block_get_payload_length (red_hdr));
GST_BUFFER_FLAG_SET (ret, GST_RTP_BUFFER_FLAG_REDUNDANT);
}
*red_hdr_offset += rtp_red_block_header_get_length (TRUE);
*red_payload_offset += rtp_red_block_get_payload_length (red_hdr);
return ret;
}
static GstBuffer *
gst_rtp_red_create_from_main_block (GstRtpRedDec * self,
GstRTPBuffer * red_rtp, gsize red_hdr_offset, gsize * red_payload_offset)
{
guint8 *payload = gst_rtp_buffer_get_payload (red_rtp);
GstBuffer *ret = gst_rtp_red_create_packet (self, red_rtp,
gst_rtp_buffer_get_marker (red_rtp),
rtp_red_block_get_payload_type (payload + red_hdr_offset),
gst_rtp_buffer_get_seq (red_rtp),
gst_rtp_buffer_get_timestamp (red_rtp),
*red_payload_offset, -1);
*red_payload_offset = gst_rtp_buffer_get_payload_len (red_rtp);
return ret;
}
static GstBuffer *
gst_rtp_red_create_from_block (GstRtpRedDec * self, GstRTPBuffer * red_rtp,
gsize * red_hdr_offset, gsize * red_payload_offset)
{
guint8 *payload = gst_rtp_buffer_get_payload (red_rtp);
if (rtp_red_block_is_redundant (payload + (*red_hdr_offset)))
return gst_rtp_red_create_from_redundant_block (self, red_rtp,
red_hdr_offset, red_payload_offset);
return gst_rtp_red_create_from_main_block (self, red_rtp, *red_hdr_offset,
red_payload_offset);
}
static GstFlowReturn
gst_rtp_red_process (GstRtpRedDec * self, GstRTPBuffer * red_rtp,
gsize first_red_payload_offset)
{
gsize red_hdr_offset = 0;
gsize red_payload_offset = first_red_payload_offset;
gsize payload_len = gst_rtp_buffer_get_payload_len (red_rtp);
GstFlowReturn ret = GST_FLOW_OK;
do {
GstBuffer *buf =
gst_rtp_red_create_from_block (self, red_rtp, &red_hdr_offset,
&red_payload_offset);
if (buf)
ret = gst_pad_push (self->srcpad, buf);
} while (GST_FLOW_OK == ret && red_payload_offset < payload_len);
return ret;
}
static GstFlowReturn
gst_rtp_red_dec_chain (GstPad * pad, GstObject * parent, GstBuffer * buffer)
{
GstRtpRedDec *self = GST_RTP_RED_DEC (parent);
GstRTPBuffer irtp = GST_RTP_BUFFER_INIT;
GstFlowReturn ret = GST_FLOW_OK;
gsize first_red_payload_offset = 0;
if (self->pt == UNDEF_PT)
return gst_pad_push (self->srcpad, buffer);
if (!gst_rtp_buffer_map (buffer, GST_MAP_READ, &irtp))
return gst_pad_push (self->srcpad, buffer);
gst_rtp_red_history_update (self, &irtp);
if (self->pt != gst_rtp_buffer_get_payload_type (&irtp)) {
GST_LOG_RTP_PACKET (self, "rtp header (incoming)", &irtp);
gst_rtp_buffer_unmap (&irtp);
return gst_pad_push (self->srcpad, buffer);
}
self->num_received++;
if (rtp_red_buffer_is_valid (self, &irtp, &first_red_payload_offset)) {
GST_DEBUG_RTP_PACKET (self, "rtp header (red)", &irtp);
ret = gst_rtp_red_process (self, &irtp, first_red_payload_offset);
}
gst_rtp_buffer_unmap (&irtp);
gst_buffer_unref (buffer);
return ret;
}
static void
gst_rtp_red_dec_dispose (GObject * obj)
{
GstRtpRedDec *self = GST_RTP_RED_DEC (obj);
g_queue_free_full (self->rtp_history, rtp_hist_item_free);
G_OBJECT_CLASS (gst_rtp_red_dec_parent_class)->dispose (obj);
}
static void
gst_rtp_red_dec_init (GstRtpRedDec * self)
{
GstPadTemplate *pad_template;
pad_template =
gst_element_class_get_pad_template (GST_ELEMENT_GET_CLASS (self), "src");
self->srcpad = gst_pad_new_from_template (pad_template, "src");
gst_element_add_pad (GST_ELEMENT_CAST (self), self->srcpad);
pad_template =
gst_element_class_get_pad_template (GST_ELEMENT_GET_CLASS (self), "sink");
self->sinkpad = gst_pad_new_from_template (pad_template, "sink");
gst_pad_set_chain_function (self->sinkpad,
GST_DEBUG_FUNCPTR (gst_rtp_red_dec_chain));
GST_PAD_SET_PROXY_CAPS (self->sinkpad);
GST_PAD_SET_PROXY_ALLOCATION (self->sinkpad);
gst_element_add_pad (GST_ELEMENT (self), self->sinkpad);
self->pt = DEFAULT_PT;
self->num_received = 0;
self->rtp_history = g_queue_new ();
}
static void
gst_rtp_red_dec_set_property (GObject * object, guint prop_id,
const GValue * value, GParamSpec * pspec)
{
GstRtpRedDec *self = GST_RTP_RED_DEC (object);
if (GST_LEVEL_LOG <= gst_debug_category_get_threshold (GST_CAT_DEFAULT)) {
gchar *val_str = gst_value_serialize (value);
GST_LOG_OBJECT (object, "Setting property \"%s\" to %s", pspec->name,
val_str);
g_free (val_str);
}
switch (prop_id) {
case PROP_PT:
self->pt = g_value_get_int (value);
break;
default:
G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
break;
}
}
static void
gst_rtp_red_dec_get_property (GObject * object, guint prop_id,
GValue * value, GParamSpec * pspec)
{
GstRtpRedDec *self = GST_RTP_RED_DEC (object);
switch (prop_id) {
case PROP_PT:
g_value_set_int (value, self->pt);
break;
case PROP_RECEIVED:
g_value_set_uint (value, self->num_received);
break;
default:
G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
break;
}
if (GST_LEVEL_LOG <= gst_debug_category_get_threshold (GST_CAT_DEFAULT)) {
gchar *val_str = gst_value_serialize (value);
GST_LOG_OBJECT (object, "Returning property \"%s\" %s", pspec->name,
val_str);
g_free (val_str);
}
}
static void
gst_rtp_red_dec_class_init (GstRtpRedDecClass * klass)
{
GObjectClass *gobject_class;
GstElementClass *element_class;
gobject_class = G_OBJECT_CLASS (klass);
element_class = GST_ELEMENT_CLASS (klass);
gst_element_class_add_pad_template (element_class,
gst_static_pad_template_get (&src_template));
gst_element_class_add_pad_template (element_class,
gst_static_pad_template_get (&sink_template));
gst_element_class_set_metadata (element_class,
"Redundant Audio Data (RED) Decoder",
"Codec/Depayloader/Network/RTP",
"Decode Redundant Audio Data (RED)",
"Hani Mustafa <hani@pexip.com>, Mikhail Fludkov <misha@pexip.com>");
gobject_class->set_property =
GST_DEBUG_FUNCPTR (gst_rtp_red_dec_set_property);
gobject_class->get_property =
GST_DEBUG_FUNCPTR (gst_rtp_red_dec_get_property);
gobject_class->dispose = GST_DEBUG_FUNCPTR (gst_rtp_red_dec_dispose);
g_object_class_install_property (G_OBJECT_CLASS (klass), PROP_PT,
g_param_spec_int ("pt", "payload type",
"Payload type FEC packets",
MIN_PT, MAX_PT, DEFAULT_PT,
G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
g_object_class_install_property (G_OBJECT_CLASS (klass), PROP_RECEIVED,
g_param_spec_uint ("received", "Received",
"Count of received packets",
0, G_MAXUINT32, 0, G_PARAM_READABLE | G_PARAM_STATIC_STRINGS));
GST_DEBUG_CATEGORY_INIT (gst_rtp_red_dec_debug, "rtpreddec", 0,
"RTP RED Decoder");
}
/* GStreamer plugin for forward error correction
* Copyright (C) 2017 Pexip
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*
* Author: Mikhail Fludkov <misha@pexip.com>
*/
#ifndef __GST_RTP_RED_DEC_H__
#define __GST_RTP_RED_DEC_H__
#include <gst/gst.h>
G_BEGIN_DECLS
#define GST_TYPE_RTP_RED_DEC \
(gst_rtp_red_dec_get_type())
#define GST_RTP_RED_DEC(obj) \
(G_TYPE_CHECK_INSTANCE_CAST((obj),GST_TYPE_RTP_RED_DEC,GstRtpRedDec))
#define GST_RTP_RED_DEC_CLASS(klass) \
(G_TYPE_CHECK_CLASS_CAST((klass),GST_TYPE_RTP_RED_DEC,GstRtpRedDecClass))
#define GST_IS_RTP_RED_DEC(obj) \
(G_TYPE_CHECK_INSTANCE_TYPE((obj),GST_TYPE_RTP_RED_DEC))
#define GST_IS_RTP_RED_DEC_CLASS(klass) \
(G_TYPE_CHECK_CLASS_TYPE((klass),GST_TYPE_RTP_RED_DEC))
typedef struct _GstRtpRedDec GstRtpRedDec;
typedef struct _GstRtpRedDecClass GstRtpRedDecClass;
struct _GstRtpRedDecClass {
GstElementClass parent_class;
};
struct _GstRtpRedDec {
GstElement parent;
GstPad *srcpad;
GstPad *sinkpad;
gint pt;
guint num_received;
GQueue *rtp_history;
};